Technical Abstract:
Microbially-driven processes, like mineralization, are influenced by agricultural practices through management's effects on soil temperature and moisture, and crop residue quality and distribution. Nutrients are released through mineralization of both labile SOM, produced by past year's residue inputs, and current-year crop residue inputs. Our objective was to study the effects of crop rotation and tillage on seasonal patterns of C and N in SOM fractions. We sampled no-till and chisel-plow plots of corn/soybean rotations 4 times across the growing season and determined mineralizable C and N, total C and N, and particulate organic matter (POM) C and N for 3 depth increments (0-7.5, 7.5-15, 15-30 cm). We observed strong seasonal patterns in the amount of C and N in the top 15 cm, which was affected more by crop type than tillage. Tillage influenced the depth distribution of C and N in the various fractions. Relative losses of C and N from SOM fractions were greater for the soybean plots than the corn plots. This was especially true for soybean-derived POM-N, which was reduced by 25% from April to October We found a relatively strong correlation between POM-C and mineralizable N (r2 = 0.45), whereas the correlation between POM-N and mineralizable N was weaker (r2 = 0.26). These results suggest that POM-C may be useful for predicting a soil's ability to supply N and, as such, an important soil quality indicator variable.